Stabilizing the frequency of a valve generator



June 18, 19350 E.-B. MOULLl N I STABILIZING THE FREQUENCY OF A VALVE GENERATOR Filed Oct. 4, 1935 'INHEZENT ZEESISTQNCES INVENTOR 5% 5411/04 0011/ AI'TORNEY Patented June 18, 1935 PATIENT forms srAniLizmo THE FREQUENCY or A vALv GENERATOR,

v Erio'Balliol Moullin, Oxford, England, assignor to Radio Corporation of America a corporation of Delaware Application October 4,

1933, Serial No. 092,061

'In Great Britain April 12, 1932 3 Claims.

The frequency of a self maintained thermionic valve generator depends slightly on the voltages operatingthe valve, but is always approximately equal to the natural frequency of the oscillatory circuit. The frequency is thus a function of the circuit and of the valve. The valve afiects the frequency both by the curvature of its characteristic and by the capacity of its electrodes. This invention is a device for rendering the frequency sensibly independent of the curvature of the characteristic. For simplicity of description attention will be limited toithe dynatron type of generator, but the invention is not limited to generators in which the potential of only one electrode is fluctuating. The 'dynatron generator consists of an oscillatory'circuit connected between a battery and the anode of a valve which is arranged to have a characteristic witha negative slope; if the resistance of the circuit is less than a certain value depending on the said negative slope, an alternating current is; produced of frequency approximately equal to that natural to the circuit. The currententering the anode consists of two portions, one which passes to the cathode by an electron stream, and one which passes by acapacity current. We here consider only that portion which passes by an electron stream. Let the relation between this portion i of the current .and the anode potential '0 be expressed by theequation f i=uv+pv +m +6v +sv where a, p, "y etc., are constants depending on the valve. 'If v= V1 sin pt, then on substitution we findthat 2' is of the form Iisin pt higher harmonies; where I1 is the amplitude of the fundamental, and therefore; the fundamental compo nent of HS in phasewithb. At every instant oi time"'the@alternating potential difference across the circuit is equal and opposite to the alternating potential differe'nce'of theanode and hence if 22=V sin pt, the currententering the circuit is in' phase with the potential difference across it; Accordingly, if 11 contained no higher harmonics the frequencywould necessarily bes'uchthat of the coil andC is the capacity of the condenser.

The voltage V1 sin pti produces higher-har where R. andL are'the resistance and inductance (Cl, 250-36) v essential to realize that the fractional amplitudes of these voltage harmonics are necessarily very small, since the circuit has asmall power factor. Thus if I1 and In areithe'fundamentaland the n? harmonic amplitudes of i'it is well knowntliat f 5 where F=R/pL is the power factor of the clrcuit. In gen'eral F is of the order of, 1/100 and hence in I general Vn/Vi is less than 1/n%, since In will probably be less than I1. l lence although the harmonics of i may be large," the harmonics of o are necessarily very small. Consequentlyfthe p, harmonics of v affect the harmonics of (very little and these are substantially the sameas 1f v=V1sinpt. I v 1? m -When Thereis now a. term I1 cos pt'which is in phase quadrature with the voltage across the circuitand consequently thefrequency must be greater than or less than that calculated previously; the discrepancy-is afunctionof u,-,B,')\ etc.

If V2, V3 etc. were all zero, the curve representing a half cycleofi Wouldbe symmetrical about the midordinate and would be represented. by the Fourier series i=I1 sin pt+Iz cos 2pt+I3 sin 31st etc. According to this 12 would be of the form v=V1 sin pt-i-VZ sin'Zpt-i-Va cos 3pt+V4 sin 4ptf etc. This curve for '0 is not symmetrical about the mid ordinates and will produce a current curve which is not quite symmetrical about the "40 mid ordinate. The disymmetry of the current curve must be due mainly-to a small term 1'1 cos pt, which is responsible ioitmaking the frequency dependent on or, ,6, x etc. v

If v hadbeen of the form .v=V1 sin pt+Va s 15 2pt+V3 sin 3pt+.etc. the curve wouldhave been symmetrical about the mid ordinate and the term I'l cos .ptwould. not have existed, in order-to prevent the term I1 cos pt from existing-it is necessary tochange by aquarter cycle the phase 50 of the potential differences due'to the harmonic currents produced by'the voltage V1 sin pt.- This invention consists in making the phase of "the harmonic.voltages suchjthat they do not arrest m the frequency 0ffl3he"gl'le1'&t()1'. This canbe done by arranging the oscillator circuit so that it is in acceptor resonance to the higher harmonies. Then the harmonic potential differences will have the desired phase relationship with the harmonic currents and further their amplitudes will be rendered negligible compared with their'previous value. A close approximation to this condition can be brought about by dividing the aforementioned condenser C into parallel portions and joining each in series with an in ductance such that one branch will be in resonance to the second harmonicand the other branch to the third harmonic and so on. The inductance of the branch tuned to the second harmonic should be shunted by a'small condenser which makes this branch capacitative to the, say, 4th, and higher harmonics,

If the term I1 cos pt could be prohibited entirely, then 11 could be made equal to l/LC by,

ing drawing which shows diagrammatically one formof, network suitable for use as the external anode tuning impedancein a thermionic oscillationgenerator inaccordance with thisinvention. -E1he -network shown in the accompanying drawing may be connected between the anode of a valve arranged to exhibit negative resistance (a so-called dynatron) and the positive terminal of the anode battery for said valve, the point A being connected to'the' anode of the valve and the pointB to the said positive terminal of the anode battery.,,, a v

The network shown in the accompanying figure comprises similar inductance coils of inductance L and resistance R each coil being represented in the figure as a resistance R in series with an inductance L. The maincondenser of the whole network is the condenser C1 and this is in series with a resistance P to bereferred to later- Each of four of the inductance coils has in series therewith a condenser marked C2 C3 C4 M05 and the whole network is such as to be as a whole in shunt resonance (so-called stopper resonance) to the working frequency Q n=- l The condensers C2 C3 'C4"C5 are the values given .by the following equations:

Thus the series branches consisting each of inductance Land resistance R and capacity C2 or Ca er C4 or C5 is in acceptor resonance either to the" second third, fourth, or fifth harmonic of the working ne uenc and therefore at each of thesehar'monic frequencies there willbe a branch presenting a non-inductive impedance of value R. Therefore at each of the harmonic frequencies thenetworkias awhclewill present an impedance consistingof aigpredominantly inductive or cawith the condenser C1.

pacitative impedance of high value shunted by a small resistance R which may be made so small relative to the joint impedance of the rest of the circuit that it is for practical purposes sufficient to assume that the total effective impedance between the points A and B at each of the harmonic frequencies in question is that of a non-inductive resistance of value R. At the fundamental or working frequency n each of the acceptor branches presents a capacitative impedance and is thus equivalent to a condenser added in parallel Owing, however, to the fact that each of these added capacitative branches includes a resistance R the added condenser is in effect one of relatively poor power factor. It may be calculated that at the working frequency 11. the total effect from this point of view of the acceptor branches is equivalent to that of a condenser of capacity I 34 CI+ECZ since p LK=1; K=4Cz=2.307701. Thus if the acceptor branches were removed it would be necessary to increase-the capacity of C1 to a value 2.3077C1 in order to maintain. the reduced network, (consisting of Crin parallel with LR) in stopperresonance at the frequency n. Since at the, fundamental frequency n the acceptor branches are equivalent to a portion of the total effective capacity K this capacity will have an appreciable power factor and owing to the fact that the; acceptor branch LCz carries a much greater fraction of the total capacity current than the higher harmonic acceptor branches L03 or LC4 the branch LCz will have most effect in increasing the total effective power factor. It may be calculated that the effective resistance of the whole network is 1.1325R.

The current through the higher harmonic acceptor branches is so small a fraction of the total capacity current for example, in the case illustrated and at ordinary wireless frequency, the current through the branch L05 is relatively'so small-that the energy waste therein is a negligible fraction.of the total energy loss whence it follows that the resistance of the coils of the upper harmonic acceptor branches--in the example specified the resistance of the coil in the branch L05, is not important. For operation at the shorter wave lengths the capacity required theoretically for the branch C5 may be inconven iently small and asa matter of practical convenience therefore it may be of advantage to make the coil of the branch L05 smaller than that in the other branches so as to allow C5 to .be correspondingly increased, e. g. the coil of the branch LCs may be V L.

It has been previously pointed out that stopper circuit resonance in the network as a whole will occur at the frequency given by the equation p LK =1. if the power factor of the effective condenser branch be equal to that of the effective inductive branch. The provisioncf the resistance P shown in the accompanying drawing en- .ables this requirement of equality of power factor to be satisfied, the said resistance P being in the case specifically illustrated and described of value 0.86813. With a resistance P of this value the at the fundamental frequency nwill be Although, theoretically, increased advantage will be obtained by increasing the number of acceptor branches, in practice a comparatively limited number of branches'is sufiicient and increase in the number of branches beyond a four or five branched circuit does not in ordinary circumstances substantially improve the practical results while constructional difficulties and disad: vantages are obviously increased.

Iclaim: a

1. An oscillation generation circuit comprising an electron discharge device having an electrical network in the path traversed by the oscillatory energy, said network comprising an inductive branch, a capacitive branch in parallel with said inductive branch and a plurality of series resonant branches resonant to harmonics direct ly in shunt with said inductive and capacitive branches, said network being anti-resonant to the fundamental frequency but series resonant to said harmonics.

2. A dynatron oscillation generation circuit comprising an electron discharge device including an anode, cathode, and screen grid electrode, a source of potential for maintaining said screen grid at a higher positive potential than said anode, an electrical network comprising a plurality of series branches connected in parallel located between said anode and cathode, each of said branches being resonant to a harmonic frequency of the generated energy and comprising an insenting a capacitive impedance tothe working frequency, and a main condenser in parallel with an inductance, both said maincondenser and its parallel connected inductance being in shunt relation with said parallel combination of series branches, the electrical network as awhole being anti resonant to the working frequency.

,ductance and a condenser in'series, whereby at predetermined different harmonic frequencies 3 An oscillation generation circuit comprising a multi-electrode electron discharge device including anode and cathode electrodes, an electrical network comprising a plurality of series branches connected in parallel located between said anode and cathode, each of said branches being resonant to a harmonic frequency of the generated energy and comprising an inductance and a condenser in series, whereby at predetermined different harmonicfrequencies there will be a E. B. MOULLIN. 

